Piezoelectric fan and cooling device

ABSTRACT

A piezoelectric fan includes reinforcing plates that increase the rigidity of a portion of the vibrating plate corresponding to a gap between a piezoelectric element and a fixing plate. First ends of the reinforcing plates are attached to portions of the vibrating plate on both sides of piezoelectric elements in the width direction, and second ends of the reinforcing plates are attached to a fixed end of the vibrating plate such that the second ends and the fixing plate sandwich the fixed end of the vibrating plate therebetween and such that the reinforcing plates extend over the gap. The reinforcing plates prevent vibration of the portion of the vibrating plate corresponding to the gap, prevent a portion of vibration energy generated by expansion and contraction of the piezoelectric elements from being consumed in the portion corresponding to the gap, and increase the amplitude of the vibration of blade ends.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a piezoelectric fan that dischargeswarm air from the vicinity of a heat dissipater, and to a cooling deviceincluding the piezoelectric fan.

2. Description of the Related Art

Electronic components are mounted with high density in small electronicapparatuses. Therefore, dissipation of heat generated in the apparatusesis an important issue. For example, while the size of personal computershas decreased, the CPU clock rate has increased in order to improve theprocessing performance. As a result, in such an electronic apparatus,the airflow is reduced due to the high-density mounting of componentswhile the amount of heat generated by the CPU, which is an example of aheat-generating member, has been increased. In such circumstances, ithas become an important issue to discharge warm air that is heated by aheat dissipater, such as a heatsink, which is disposed on an uppersurface of the CPU, from the vicinity of the heat dissipater so as toprevent an increase in the temperature of the CPU.

For example, Hiroto Kaneko, “Demonstration of Heatsink that Blows Air byVibration”, Sep. 25, 2009, Nikkei WinPC, searched on Oct. 16, 2009 onthe Internet,<URL:http://pc.nikkeibp.co.jp/article/news/20090925/1018872/?f=news>(hereinafter referred to as “Kaneko”) describes a piezoelectric fan thatdischarges warm air from the spaces between heat-dissipating fins of aheatsink. Referring to FIGS. 1 to 3B, the structures of thepiezoelectric fan and the cooling device described in Kaneko will bedescribed.

FIG. 1 is a perspective view of a piezoelectric fan 10 described inKaneko. FIG. 2 is a side view of the piezoelectric fan 10. FIGS. 3A and3B are perspective views of a cooling device 9 including thepiezoelectric fan 10 described in Kaneko. The piezoelectric fan 10includes a vibrating plate 11, piezoelectric elements 12A and 12B, and afixing plate 13. A heatsink 20 includes heat-dissipating fins 22 thatextend upward from a base portion 21 so as to be parallel to each other.In FIGS. 3A and 3B, a heat-generating member 50, such as a CPU, ismounted on a circuit board. The heatsink 20 is disposed on the uppersurface of the heat-generating member 50 so that the bottom surface ofthe heatsink 20 is thermally coupled to the upper surface. The coolingdevice 9 is formed by fixing the piezoelectric fan 10 to the heatsink 20that is made of aluminum.

As illustrated in FIGS. 1 and 2, the two piezoelectric elements 12A and12B are affixed to both sides of the vibrating plate 11, and thevibrating plate 11 bends when the piezoelectric elements 12A and 12Bexpand and contract. Blades 14 are provided on a free end side of thevibrating plate 11, and the blades 14 vibrate when the vibrating plate11 bends. The fixing plate 13 is fixed to a fixed end of the vibratingplate 11.

The two piezoelectric elements 12A and 12B are affixed to the vibratingplate 11 so as to sandwich the vibrating plate 11, which functions as anintermediate electrode, therebetween. Thus, the piezoelectric elements12A and 12B and the vibrating plate 11 define a bimorph vibrator. Eachof the piezoelectric elements 12A and 12B includes a film electrode thatis provided on the surface of piezoelectric ceramic body thereof. When adrive voltage is applied between the film electrodes and the vibratingplate 11, which functions as an intermediate electrode, the vibratingplate 11 is warped in the longitudinal direction and vibrates.

The two piezoelectric elements 12A and 12B are arranged such that thepiezoelectric element 12B contacts the fixing plate 13 and such that thepiezoelectric elements 12A and 12B sandwich a portion of the vibratingplate 11 therebetween. Then, the piezoelectric elements 12A and 12B areaffixed to the vibrating plate 11 (see FIGS. 1 and 2). Each of the sevenblades 14 is inserted in a corresponding one of the grooves between theheat-dissipating fins 22 of the heatsink 20 (see FIG. 3A and 3B), andthe fixed end of the vibrating plate 11 is fixed, using screws 15, to anupper portion of the heatsink 20 with the fixing plate 13 therebetween.

With the structure described in Kaneko, heat that is generated by theheat-generating member 50 is transferred to the heatsink 20, and air inthe spaces between the heat-dissipating fins 22 is heated by theheat-dissipating fins 22. When the piezoelectric fan 10 is driven, theblades 14 vibrate and discharge the warm air from the spaces between theheat-dissipating fins 22.

However, even when the fixing plate 13 and the piezoelectric elements12A and 12B are affixed to the vibrating plate 11 after being positionedas described above, a gap G is generated between the fixing plate 13 andthe piezoelectric elements 12A and 12B (see FIG. 2). This is becausethere is a limitation on the precision of positioning or because thereare microscopic asperities on the surface of the fixing plate 13.

As shown in FIG. 2, the rigidity of a portion of the vibrating plate 11corresponding to the gap G depends only on the rigidity of the vibratingplate 11. Therefore, the rigidity of this portion is less than therigidity of a portion of the vibrating plate 11 to which the fixingplate 13 is bonded and the rigidity of a portion of the vibrating plate11 to which the piezoelectric elements 12A and 12B are bonded.Accordingly, the inventors of the present invention discovered that,with the piezoelectric fan 10 described in Kaneko, the portion of thevibrating plate 11 corresponding to the gap G vibrates, and a portion ofthe vibration energy that is generated by expansion and contraction ofthe piezoelectric elements 12A and 12B is consumed in the portioncorresponding to the gap G, and thereby the amplitude of the vibrationof the ends of the blades 14 is decreased. That is, the gap G impairsthe air-moving performance of the piezoelectric fan 10.

Therefore, when the piezoelectric fan 10 described in Kaneko is mountedon the heatsink 20, the piezoelectric fan 10 may not sufficientlydissipate heat from the heat-dissipating fins 22. Because a variety ofhigh-speed CPUs, which generate a large amount of heat, have been usedrecently, a piezoelectric fan having a cooling performance that isgreater than that of the piezoelectric fan 10 described Kaneko isdesired.

SUMMARY OF THE INVENTION

To overcome the problems described above, preferred embodiments of thepresent invention provide a piezoelectric fan with which the air-movingperformance of a vibrating plate is increased and thereby the coolingperformance is improved, and also provide a cooling device including thepiezoelectric fan.

According to a preferred embodiment of the present invention, apiezoelectric fan preferably includes a piezoelectric element thatexpands and contracts in accordance with a voltage applied thereto, avibrating plate to which the piezoelectric element is attached, thevibrating plate bending and vibrating at a resonant frequency when thepiezoelectric element expands and contracts, a fixing member that fixesa fixed end of the vibrating plate to another member, and a reinforcingmember arranged on the vibrating plate such that, when the vibratingplate is viewed in a side view in a direction in which a boundarybetween the piezoelectric element and the fixing member is visible, afirst end of the reinforcing member is disposed on a portion of thevibrating plate to which the piezoelectric element is bonded, and asecond end of the reinforcing member is disposed on a portion of thevibrating plate to which the fixing member is bonded.

With this structure, heat generated by the heat-generating member istransferred to the heat dissipater, and the heat dissipater generateswarm air in the vicinity of the heat dissipater. Preferably, the heatdissipater is, for example, a heatsink or a heat spreader. With thisstructure, the piezoelectric fan is directly fixed to the heatdissipater or fixed to another member, and the warm air is dischargedfrom the vicinity of the heat dissipater due to vibration of thevibrating plate.

Because the reinforcing member is preferably arranged at the positiondescribed above, the rigidity of a portion of the vibrating platecorresponding to the gap between the piezoelectric element and thefixing member is increased, and the following phenomenon occurs. Thatis, the reinforcing member prevents vibration of the portion of thevibrating plate corresponding to the gap G, and prevents a portion ofvibration energy that is generated by expansion and contraction of thepiezoelectric element from being consumed in the portion correspondingto the gap G, and thereby the amplitude of the vibration of the freeends of the vibrating plate is significantly increased. Thus, theair-moving performance of the piezoelectric fan is significantlyincreased.

Therefore, with the piezoelectric fan having this structure, theair-moving performance of the vibrating plate and the coolingperformance are significantly increased.

According to a preferred embodiment of the present invention, the firstend of the reinforcing member is preferably attached to each side in thewidth direction of the portion of the vibrating plate to which thepiezoelectric element is attached, and the second end of the reinforcingmember is preferably attached to the fixed end of the vibrating platesuch that the second end and the fixing member sandwich the fixed end ofthe vibrating plate therebetween.

According to another preferred embodiment of the present invention, thereinforcing member is preferably a portion of the fixing member, and thefirst end of the reinforcing member is preferably attached to each sidein the width direction of a portion of the vibrating plate to which thepiezoelectric element is attached.

According to another preferred embodiment of the present invention, thefirst end of the reinforcing member is preferably attached to an end ofthe piezoelectric element near the fixing member, and the second end ofthe reinforcing member is bonded to the fixed end of the vibrating platesuch that the second end and the fixing member sandwich the fixed end ofthe vibrating plate therebetween.

According to another preferred embodiment of the present invention, thevibrating plate preferably includes a cut-out portion on each side inthe width direction of the portion to which the piezoelectric element isbonded.

With this structure, an openings or a cut-out portion is provided oneach side of a portion of the vibrating plate to which the piezoelectricelement is attached.

According to another preferred embodiment of the present invention, thefirst end of the reinforcing member is preferably attached to thevibrating plate such that the first end and the piezoelectric elementsandwich the vibrating plate therebetween, and the second end of thereinforcing member is preferably attached to the fixed end of thevibrating plate such that the second end and the fixing member sandwichthe fixed end of the vibrating plate therebetween.

This structure is preferably used when the piezoelectric element and thevibrating plate define a unimorph vibrator.

The number of the piezoelectric elements is preferably two, for example,and the piezoelectric elements sandwich the vibrating platetherebetween.

In this case, the piezoelectric elements and the vibrating platepreferably define a bimorph vibrator. With this structure, the bendingdisplacement relative to the applied voltage is increased and theamplitude of the vibration of the vibrating plate is increased.Therefore, the air-moving performance of the piezoelectric fan isfurther increased.

The fixing member is preferably fixed to a heat dissipater thatdissipates heat that is generated by a heat-generating member.

With this structure, the piezoelectric fan is fixed to the heatdissipater and discharges warm air from the vicinity of the vibratingplate due to vibration of the vibrating plate.

According to another preferred embodiment of the present invention, acooling device preferably includes the piezoelectric fan according to apreferred embodiment of the present invention and the heat dissipater,wherein the heat dissipater is preferably a heat sink including aplurality of heat-dissipating fins, the vibrating plate preferablyincludes a plurality of blades provided on a free end side thereof, andthe fixing member preferably fixes the fixed end of the vibrating plateto an upper portion of the heatsink such that each of the plurality ofblades is inserted in a corresponding one of grooves between theplurality of heat-dissipating fins of the heatsink.

With this structure, the cooling device produces the same effect as thatof the piezoelectric fan described above.

According to another preferred embodiment of the present invention, eachof the plurality of blades of the vibrating plate is preferably benttoward the grooves between the heat-dissipating fins.

With this structure, the plurality of blades are bent toward the groovesbetween heat-dissipating fins. Therefore, a low profile cooling deviceis provided, so that the cooling performance can be increased withoutincreasing the overall size of the cooling device.

With various preferred embodiments of the present invention, theair-moving performance of the vibrating plate and the coolingperformance are significantly increased.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a piezoelectric fan of the related art.

FIG. 2 is a side view of the piezoelectric fan of the related art.

FIGS. 3A and 3B are perspective views of a cooling device including apiezoelectric fan of the related art.

FIG. 4 is a perspective view of a piezoelectric fan according to a firstpreferred embodiment of the present invention.

FIG. 5 is a side view of the piezoelectric fan according to the firstpreferred embodiment of the present invention.

FIGS. 6A and 6B are perspective views of a cooling device including thepiezoelectric fan according to the first preferred embodiment of thepresent invention.

FIG. 7 is a graph illustrating the relationship between the distancefrom a fixed end of a vibrating plate of the piezoelectric fan to aposition on the vibrating plate and the displacement of the vibratingplate at the position.

FIG. 8A is a top view of a fixing plate of a piezoelectric fan accordingto a second preferred embodiment of the present invention, FIG. 8B is afront view of the fixing plate, and FIG. 8C is a side view of the fixingplate.

FIG. 9 is a top view of the piezoelectric fan according to the secondpreferred embodiment of the present invention.

FIG. 10 is a side view of the piezoelectric fan according to the secondpreferred embodiment of the present invention.

FIG. 11 is a perspective view of a modification of the piezoelectric fanof the related art.

FIG. 12 is a perspective view of a piezoelectric fan according to athird preferred embodiment of the present invention.

FIG. 13 is a side view of the piezoelectric fan according to the thirdpreferred embodiment of the present invention.

FIGS. 14A and 14B are perspective views of a cooling device includingthe piezoelectric fan according to the third preferred embodiment of thepresent invention.

FIG. 15A is a perspective view of a piezoelectric fan according toanother preferred embodiment of the present invention, and FIG. 15B is aperspective view of a piezoelectric fan according to another preferredembodiment of the present invention.

FIG. 16A is a perspective view of a piezoelectric fan according toanother preferred embodiment of the present invention, and FIG. 16B is aside view of the piezoelectric fan according to the other preferredembodiment of the present invention.

FIG. 17A is a perspective view of a piezoelectric fan according toanother preferred embodiment of the present invention, and FIG. 17B is aside view of the piezoelectric fan according to the other preferredembodiment of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First PreferredEmbodiment

Hereinafter, a piezoelectric fan according to a first preferredembodiment of the present invention will be described.

FIG. 4 is a perspective view of a piezoelectric fan 101 according to thefirst preferred embodiment, and FIG. 5 is a side view of thepiezoelectric fan 101. FIGS. 6A and 6B are perspective views of acooling device 1 including the piezoelectric fan 101. In FIG. 5, avibrating plate is seen in side view in a direction in which theboundary between piezoelectric elements and a fixing member is visible.A gap G is illustrated in a slightly enlarged scale for convenience ofillustration.

The piezoelectric fan 101 include a vibrating plate 111, piezoelectricelements 112A and 112B, a fixing plate 113, and reinforcing plates 151and 152. A heatsink 20 preferably includes heat-dissipating fins 22 thatextend upward from the base portion 21 so as to be parallel to eachother. In FIGS. 6A and 6B, a heat-generating member 50 (heat-generatingcomponent), such as a CPU, for example, is mounted on a circuit board Pso that the bottom surface of the heatsink 20 is thermally coupled tothe upper surface of the heat-generating member 50. The cooling device 1includes the piezoelectric fan 101 and the heatsink 20, which ispreferably made of aluminum, for example.

As illustrated in FIGS. 4 and 5, two piezoelectric elements 112A and112B are affixed to both sides of the vibrating plate 111. The vibratingplate 111 bends when the piezoelectric elements 112A and 112B expand andcontract. Seven blades 141, for example, are preferably provided on thefree end side of the vibrating plate 111. The seven blades 141 vibratedue to bending of the vibrating plate 111. The seven blades 141 of thevibrating plate 111 are preferably bent at 90 degrees, for example,toward grooves between the heat-dissipating fins 22.

The vibrating plate 111 is preferably a stainless steel plate having thefollowing dimensions: a total width (i.e., the width of the seven blades141) of about 45 mm, a width of each blade of about 2.0 mm, a totallength of about 50 mm, a length from the fixed end of the vibratingplate 111 to the edge of the vibrating plate 111 (i.e., the bentportion) of about 25 mm, a length from the ends of the seven blades 141to the edge (i.e., bent portion) of the vibrating plate 111 of about 25mm, and a thickness of about 0.1 mm, for example.

Each of the piezoelectric elements 112A and 112B preferably has thefollowing dimensions: a width of about 30 mm, a length of about 15 mm,and a thickness of about 0.05 mm, for example. The two piezoelectricelements 112A and 112B are affixed to the vibrating plate 111 so as tosandwich the vibrating plate 111, which functions as an intermediateelectrode, therebetween. Thus, the piezoelectric elements 112A and 112Band the vibrating plate 111 preferably define a bimorph vibrator, forexample. Each of the piezoelectric elements 112A and 112B preferablyincludes a film electrode, for example, that is provided on the frontand back surfaces of the piezoelectric ceramic body thereof. Thepiezoelectric elements 112A and 112B are preferably poled such that,when a drive voltage in accordance with the polarization directions ofthe piezoelectric elements 112A and 112B is applied between the filmelectrodes and the vibrating plate 111, which functions as anintermediate electrode, the vibrating plate 111 is warped in thelongitudinal direction and vibrates. Because the vibrator preferably hasthe bimorph structure, the bending displacement of the vibrating plate111 relative to the voltages applied to the piezoelectric elements 112Aand 112B is increased, whereby the amplitude of the vibration of theblades 141 is more efficiently increased.

The two piezoelectric elements 112A and 112B are preferably arrangedsuch that the piezoelectric element 112B contacts the fixing plate 113and such that the piezoelectric elements 112A and 112B sandwich aportion of the vibrating plate 111 therebetween. Then, the piezoelectricelements 112A and 112B are affixed to the vibrating plate 111 (see FIGS.4 and 5). The fixing plate 113 is preferably made of glass epoxy, forexample, and preferably has the following dimensions: a width of about50 mm, a length of about 5 mm, and a thickness of about 2 mm, forexample. Each of the seven blades 141 is inserted in a corresponding oneof the grooves between the heat-dissipating fins 22 of the heatsink 20(see FIGS. 6A and 6B), and the fixed end of the vibrating plate 111 isfixed, preferably using screws 115, for example, to an upper portion ofthe heatsink 20 with the fixing plate 113 therebetween.

As a result, the gap G is generated in the piezoelectric fan 101 of thefirst preferred embodiment (see FIG. 5), in a similar manner to thepiezoelectric fan 10 of the Kaneko. That is, even when the fixing plate113 and the piezoelectric elements 112A and 112B are affixed to thevibrating plate 111 after being positioned, the gap G is generatedbetween the fixing plate 113 and the piezoelectric elements 112A and112B. This is because there is a limitation on the precision ofpositioning and/or because there are microscopic asperities on thesurface of the fixing plate 113.

Therefore, the piezoelectric fan 101 according to the first preferredembodiment includes the reinforcing plates 151 and 152, which arepreferably made of stainless steel, for example, so that the rigidity ofa portion of the vibrating plate 111 corresponding to the gap G isincreased. First ends of the reinforcing plates 151 and 152 arepreferably attached to both sides in the width direction of a portion ofthe vibrating plate 111 to which the piezoelectric elements 112A and112B are bonded. Second ends of the reinforcing plates 151 and 152 arepreferably attached to the fixed end of the vibrating plate 111 suchthat the reinforcing plates 151 and 152 and the fixing plate 113sandwich the fixed end of the vibrating plate 111 therebetween. Each ofthe reinforcing plates 151 and 152 preferably has a thickness of about0.05 mm, for example.

With the structure described above, heat that is generated by theheat-generating member 50 is transferred to the heatsink 20, and air inthe spaces between the heat-dissipating fins 22 is heated by theheat-dissipating fins 22. Each of the seven blades 141 of thepiezoelectric fan 10 vibrates between a corresponding pair of theheat-dissipating fins 22 that are next to each other without contactingthe heat-dissipating fins 22. Thus, the piezoelectric fan 101 dischargesthe warm air from the spaces between the heat-dissipating fins 22.

A comparison between the air-moving performance of the piezoelectric fan10 of Kaneko and the air-moving performance of the piezoelectric fan 101of the first preferred embodiment will be described below.

FIG. 7 is a graph illustrating the relationship between the distancefrom a fixed end of a vibrating plate of the piezoelectric fan to aposition on the vibrating plate and the displacement of the vibratingplate at the position. This graph illustrates the results of anexperiment. In the experiment, the amplitude of the vibration of ends ofthe blades was measured when a sinusoidal alternating voltage of 24 Vppat the resonant frequency was applied between the electrodes of thepiezoelectric elements and the vibrating plate of each of thepiezoelectric fan 10 and the piezoelectric fan 101.

In the experiment, the vibrating plate 11, the piezoelectric elements12A and 12B, and the fixing plate 13 of the piezoelectric fan 10,respectively, had the same dimensions and were made of the samematerials as those of the vibrating plate 111, the piezoelectricelements 112A and 112B, and the fixing plate 113 of the piezoelectricfan 101.

According to the results of the experiment, for the piezoelectric fan 10of Kaneko, the average amplitude of the vibrations of the ends of theblades was about 8.0 mm at the resonant frequency of about 89.1 Hz. Incontrast, for the piezoelectric fan 101 of the first preferredembodiment, the average amplitude of the vibrations of the ends of theblades was significantly increased to about 8.9 mm at the resonantfrequency of about 95.5 Hz. This experiment shows that the averageamplitude and the frequency of the piezoelectric fan 101 of the firstpreferred embodiment were greater than those of the piezoelectric fan 10of Kaneko. Therefore, the air-moving performance of the blades of thepiezoelectric fan of the first preferred embodiment, which isrepresented by “average amplitude×frequency”, was significantlyimproved.

This result is presumably due to the following phenomenon, which occursbecause the rigidity of the portion of the vibrating plate 111corresponding to the gap G is increased preferably by providing thereinforcing plates 151 and 152 on the vibrating plate 111. That is, thereinforcing plates 151 and 152 prevent the vibration of the portion ofthe vibrating plate 111 corresponding to the gap G and thereby prevent aportion of vibration energy, which is generated due to expansion andcontraction of the piezoelectric elements 112A and 112B, from beingconsumed in the portion corresponding to the gap G, and therebyincreases the amplitude of the vibrations of the ends of the blades 141.

As heretofore described, the blades 141 of the piezoelectric fan 101 ofthe first preferred embodiment have an air-moving performance greaterthan that of the blades of the piezoelectric fan 10, whereby the coolingperformance is significantly increased.

The vibrating plate 111, which has a relatively large overall length, isbent so that a low-profile cooling device 1 is provided, whereby thecooling performance is increased without significantly increasing thesize of the cooling device 1.

Second Preferred Embodiment

FIG. 8A is a top view of a fixing plate 213 of a piezoelectric fan 201according to a second preferred embodiment of the present invention,FIG. 8B is a front view of the fixing plate 213, and FIG. 8C is a sideview of the fixing plate 213. FIG. 9 is a top view of the piezoelectricfan 201 according to the second preferred embodiment. FIG. 10 is a sideview of the piezoelectric fan 201. In FIG. 10, a vibrating plate isshown in a side view in a direction in which the boundary betweenpiezoelectric elements and a fixing member is visible.

The piezoelectric fan 101 according to the first preferred embodimentincludes the reinforcing plates 151 and 152 arranged to increase therigidity of the portion of the vibrating plate 111 corresponding to thegap G. The piezoelectric fan 201 according to the second preferredembodiment includes the fixing plate 213 preferably made of glass epoxy,for example, which is illustrated in FIGS. 8A to 8C. The fixing plate213 preferably includes reinforcing portions 214A and 214B. First endsof the reinforcing portions 214A and 214B are preferably attached, so asto extend over the gap G, to both sides of the portion of the vibratingplate 111 to which the piezoelectric elements 112A and 112B areattached.

A comparison between the air-moving performance of the piezoelectric fan10 of Kaneko and the air-moving performance of the piezoelectric fan 201of the second preferred embodiment will be described below based on theresults of an experiment. In the experiment, the amplitude of thevibration of ends of the blades was measured when a sinusoidalalternating voltage of about 24 Vpp at the resonant frequency wasapplied between the electrodes of the piezoelectric elements and thevibrating plate of each of the piezoelectric fan 10 and thepiezoelectric fan 201.

In the experiment, the vibrating plate 11, the piezoelectric elements12A and 12B, and the fixing plate 13 of the piezoelectric fan 10respectively had the same or substantially the same dimensions and weremade of the same or substantially the same materials as those of thevibrating plate 111, the piezoelectric elements 112A and 112B, and thefixing plate 213 (excluding the reinforcing portions 214A and 214B) ofthe piezoelectric fan 201.

According to the result of the experiment, for the piezoelectric fan 10of Kaneko, the average amplitude of the vibrations of the ends of theblades was about 8.0 mm at the resonant frequency of about 89.1 Hz. Incontrast, for the piezoelectric fan 201 of the second preferredembodiment, the average amplitude of the vibrations of the ends of theblades was increased to about 8.6 mm at the resonant frequency of about89.8 Hz. That is, the average amplitude and the frequency of thepiezoelectric fan 201 of the second preferred embodiment were greaterthan those of the piezoelectric fan 10 of. Therefore, the air-movingperformance of the blades of the piezoelectric fan according to thesecond preferred embodiment was significantly improved.

This result is presumably due to the same phenomenon as that for thepiezoelectric fan 101 of the first preferred embodiment, which occursbecause the rigidity of the portion of the vibrating plate 111corresponding to the gap G is increased by attaching the reinforcingportions 214A and 214B of the fixing plate 213 to the vibrating plate111.

As heretofore described, the blades 141 of the piezoelectric fan 201 ofthe second preferred embodiment have an air-moving performance greaterthan that of the blades of the piezoelectric fan 10, whereby the coolingperformance is significantly increased. Therefore, when a cooling deviceincludes the fixed end of the vibrating plate 111 of the piezoelectricfan 201 of the second preferred embodiment fixed to an upper portion ofthe heatsink 20 as illustrated in FIGS. 6A and 6B, the coolingperformance of the cooling device is significantly increased.

The vibrating plate 111 is preferably bent so that a low-profile coolingdevice is provided, whereby the cooling performance can be increasedwithout increasing the size of the cooling device.

Third Preferred Embodiment

FIG. 11 is a perspective view of a piezoelectric fan 30, which is amodification of the piezoelectric fan 10 described in Kaneko. FIG. 12 isa perspective view of a piezoelectric fan 301 according to a thirdpreferred embodiment of the present invention. FIG. 13 is a side view ofthe piezoelectric fan 301 according to the third preferred embodiment.FIGS. 14A and 14B are perspective views of a cooling device 3 includingthe piezoelectric fan 301 according to the third preferred embodiment.In FIG. 13, a vibrating plate is shown in side view in a direction inwhich the boundary between piezoelectric elements and a fixing member isvisible.

First, in order to compare the air-moving performance of thepiezoelectric fan 301 of the third preferred embodiment with theair-moving performance of the piezoelectric fan 30, which is amodification of the piezoelectric fan 10, the structure of thepiezoelectric fan 30 will be described.

The piezoelectric fan 30 differs from the piezoelectric fan 10 in theshape of the vibrating plate. In other respects, the piezoelectric fan30 and the piezoelectric fan 10 have the same or substantially the samestructure. As illustrated in FIG. 11, a vibrating plate 311 is astainless steel plate preferably having the following dimensions: awidth of about 45 mm, a length of about 50 mm, and a thickness of about0.1 mm, for example. Cut-out portions 118 are formed by punch pressingthe stainless steel plate. To be specific, the cut-out portions 118 areprovided on both sides of a portion of the vibrating plate 311 to whichthe piezoelectric elements 112A are 112B are affixed, i.e., both sidesin a direction perpendicular or substantially perpendicular to thelongitudinal direction of the blades. The width the portion of thevibrating plate 311 to which the piezoelectric elements 112A and 112Bare affixed is about 35 mm. Other dimensions of the vibration plate 311are the same as those of the vibrating plate 111.

The piezoelectric fan 301 of the third preferred embodiment, which isillustrated in FIGS. 12 and 13, differs from the piezoelectric fan 30 ofthe comparative example in that the piezoelectric fan 301 includes areinforcing plate 313, which is preferably made of glass epoxy, forexample, in order to increase the rigidity of a portion of the vibratingplate 311 corresponding to the gap G. In other respects, thepiezoelectric fan 301 and the piezoelectric fan 30 have the same orsubstantially the same structure. A first end of the reinforcing plate313 is preferably attached to an end of the piezoelectric element 112Anear the fixing plate 113. A second end of the reinforcing plate 313 ispreferably attached to the fixed end of the vibrating plate 311 suchthat the reinforcing plate 313 and the fixing plate 113 sandwich thefixed end of the vibrating plate 311 therebetween. The thickness of thereinforcing plate 313 is preferably about 0.1 mm, for example.

Next, a comparison between the air-moving performance of thepiezoelectric fan 30 the air-moving performance of the piezoelectric fan301 of the third preferred embodiment will be described based on theresults of an experiment. In the experiment, the amplitude of thevibration of ends of the blades was measured when a sinusoidalalternating voltage of about 24 Vpp at the resonant frequency wasapplied between the electrodes of the piezoelectric elements and thevibrating plate of each of the piezoelectric fan 30 and thepiezoelectric fan 301.

According to the results of the experiment, for the piezoelectric fan30, the average amplitude of the vibrations of the ends of the bladeswas about 9.0 mm at the resonant frequency of about 82.0 Hz. Incontrast, for the piezoelectric fan 301 of the third preferredembodiment, the average amplitude of the vibrations of the ends of theblades was increased to about 9.5 mm at the resonant frequency of about84.1 Hz. That is, this experiment shows that the average amplitude andthe frequency of the piezoelectric fan 301 of the third preferredembodiment were larger than those of the piezoelectric fan 30.Therefore, the air-moving performance of the blades of the piezoelectricfan 301 according to the third preferred embodiment was significantlyimproved.

This result is presumably due to the same phenomenon as that for thepiezoelectric fan 101 of the first preferred embodiment, which occursbecause the rigidity of the portion of the vibrating plate 311corresponding to the gap G is increased by providing the reinforcingplate 313 on the vibrating plate 311.

Next, the airflow in the piezoelectric fan 301 will be described. Asillustrated in FIGS. 14A and 14B, each of the seven blades 141 areinserted in a corresponding one of the grooves between theheat-dissipating fins 22 of the heatsink 20, the cut-out portions 118are preferably arranged above the grooves between the heat-dissipatingfins 22, and the fixed end of the vibrating plate 311 is preferablyfixed to an upper portion of the heatsink 20. Thus, in the thirdpreferred embodiment, the cooling device 3 including the piezoelectricfan 301 and the heatsink 20 is provided. With this structure, when thepiezoelectric fan 301 is driven and the blades 141 vibrate, airflow isproduced due to the existence of the cut-out portions 118 as follows.That is, cool air flows downward through the cut-out portions 118 intothe grooves between the heat-dissipating fins 22 and warm air generatedbetween the heat-dissipating fins 22 flows upward through the cut-outportions 118. Therefore, with the piezoelectric fan 301 of the thirdpreferred embodiment, not only the air-moving performance of thepiezoelectric fan 301 but also the airflow to the heat-dissipating fins22 are significantly improved.

As heretofore described, with the piezoelectric fan 301 of the thirdpreferred embodiment, the air-moving performance of the blades 141 andthe airflow to the heat-dissipating fins 22 are improved, whereby thecooling performance is significantly improved.

The vibrating plate 311 is preferably bent so that a low-profile coolingdevice is provided, whereby the cooling performance can be increasedwithout increasing the size of the cooling device.

In the preferred embodiments of the present invention described above,the piezoelectric fans 101, 201, and 301 preferably include thevibrating plate 111 and the vibrating plate 311 that are bent towardsthe grooves between the heat-dissipating fins 22. However, asillustrated in FIG. 15A, a piezoelectric fan 401, which includes thevibrating plate 111 or the vibrating plate 311 that is preferably notbent, may be used. Alternatively, as illustrated in FIG. 15B, apiezoelectric fan 501, which includes the vibrating plate 111 or thevibrating plate 311 that is preferably bent at an appropriate angle (forexample, 45 degrees), may be used.

In the preferred embodiments of the present invention described above,the piezoelectric fans 101, 201, and 301 are preferably bimorph-typepiezoelectric fans, in which the piezoelectric elements 112A and 112Bare attached to both sides of the vibrating plate 111. However, asillustrated in FIGS. 16A and 16B, a unimorph piezoelectric fan 601,which includes the vibrating plate 111 and only one piezoelectricelement 112A that is attached to the upper surface of the vibratingplate 111, may be used. Alternatively, as illustrated in FIGS. 17A and17B, a unimorph piezoelectric fan 701, which includes the vibratingplate 111 and only a piezoelectric element 112B that is attached to thelower surface of the vibrating plate 111, may preferably be used.

The piezoelectric fan 701 includes, instead of the reinforcing plates151 and 152, a reinforcing plate 153 that is preferably made ofstainless steel, for example. The reinforcing plate 153 is preferablyattached to the upper surface of the vibrating plate 111 such that afirst end of the reinforcing plate 153 is located at a positioncorresponding to a portion of the vibrating plate 111 to which thepiezoelectric element 112B is attached and a second end of thereinforcing plate 153 is located at a position corresponding to aportion of the vibrating plate 111 to which the fixing plate 113 isattached.

In the preferred embodiments of the present invention described above,each of the vibrating plate 111 and the vibrating plate 311 preferablyincludes a plurality of blades provided on the free end side thereof.However, a vibrating plate including a free end that is not branchedinto a plurality of blades may be used.

In the preferred embodiments of the present invention described above,the blades 141 need not be made of stainless steel, and may preferablybe made of an elastic metal, such as phosphor bronze, or a resin, forexample.

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

1. A piezoelectric fan comprising: a piezoelectric element arranged toexpand and contract in accordance with a voltage applied thereto; avibrating plate to which the piezoelectric element is attached, thevibrating plate being arranged to bend and vibrate at a resonantfrequency when the piezoelectric element expands and contracts; a fixingmember arranged to fix a fixed end of the vibrating plate to anothermember; and a reinforcing member arranged on the vibrating plate suchthat, when the vibrating plate is viewed in a side view in a directionin which a boundary between the piezoelectric element and the fixingmember is visible, a first end of the reinforcing member is located on aportion of the vibrating plate to which the piezoelectric element isattached, and a second end of the reinforcing member is located on aportion of the vibrating plate to which the fixing member is attached.2. The piezoelectric fan according to claim 1, wherein the first end ofthe reinforcing member is attached to each side in a width direction ofthe portion of the vibrating plate to which the piezoelectric element isattached, and the second end of the reinforcing member is attached tothe fixed end of the vibrating plate such that the second end and thefixing member sandwich the fixed end of the vibrating platetherebetween.
 3. The piezoelectric fan according to claim 1, wherein thereinforcing member is a portion of the fixing member, and the first endof the reinforcing member is attached to each side in a width directionof a portion of the vibrating plate to which the piezoelectric elementis attached.
 4. The piezoelectric fan according to claim 1, wherein thefirst end of the reinforcing member is attached to an end of thepiezoelectric element near the fixing member, and the second end of thereinforcing member is attached to the fixed end of the vibrating platesuch that the second end and the fixing member sandwich the fixed end ofthe vibrating plate therebetween.
 5. The piezoelectric fan according toclaim 4, wherein the vibrating plate includes a cut-out portion on eachside in a width direction of the portion to which the piezoelectricelement is attached.
 6. The piezoelectric fan according to claim 1,wherein the first end of the reinforcing member is attached to thevibrating plate such that the first end and the piezoelectric elementsandwich the vibrating plate therebetween, and the second end of thereinforcing member is attached to the fixed end of the vibrating platesuch that the second end and the fixing member sandwich the fixed end ofthe vibrating plate therebetween.
 7. The piezoelectric fan according toclaim 1, wherein a number of the piezoelectric elements is two, and thepiezoelectric elements sandwich the vibrating plate therebetween.
 8. Thepiezoelectric fan according to claim 1, wherein the fixing member isfixed to a heat dissipater that dissipates heat that is generated by aheat-generating member.
 9. A cooling device comprising: piezoelectricfan according to claim 8; and the heat dissipater; wherein the heatdissipater is a heatsink including a plurality of heat-dissipating fins;the vibrating plate includes a plurality of blades provided on a freeend side thereof; and the fixing member fixes the fixed end of thevibrating plate to an upper portion of the heatsink such that each ofthe plurality of blades is inserted in a corresponding one of groovesbetween the plurality of heat-dissipating fins of the heatsink.
 10. Thecooling device according to claim 9, wherein the plurality of blades ofthe vibrating plate are bent toward the grooves between theheat-dissipating fins.